“War of the Worlds” is approximately two hours long. Not one second is less than masterly, and a good many are literally stunning. When the aliens rise to destroy mankind, they do so armed with laser beams, spotlights, strobe bulbs, multicolored flares, massive bolts of lightning – a blazing arsenal to overwhelm the sun. Secured in their gigantic insectoid robots, they also come with boom, thunder, and an unnerving ambient drone, their every attack preceded by a pulverizing blast of their otherworldly foghorn.

As sight, the alien invasion is dazzling; as sound, it will turn your bones to jelly. Here is one of the consummate sensory onslaughts in modern popular cinema. For 60-odd minutes, “War of the Worlds” straps you into a thrill ride of unrelenting excitement and terror. This is supremely riveting entertainment, apocalyptic sci-fi par excellence. Were the intensity level sustained, we’d have one for the ages.

As it happens, things go slack in the third act. The last half-hour wobbles. Then, in the final minutes, doomsday arrives: This bleakest of blockbusters resolves on the most reactionary note imaginable. Pulled back from the brink of annihilation, mankind is preserved with an affirmation of the status quo so shamelessly cheesy, so appallingly retrograde, it makes the climactic cuddle of “AI” look like the blackest depths of despair.

Another Steven Spielberg movie, another conundrum.

The story is simple, the allegory explicit. Tom Cruise plays Ray Ferrier – dockworker, deadbeat dad, and idiot-grinning man-boy. Ray’s ex-wife (Miranda Otto), accompanied by her ultra-bourgeois boyfriend, drops off the kids for a weekend visit. Rachel (Dakota Fanning), his young daughter, is a budding hipster neurotic and vegetarian. Robbie (Justin Chatwin), his teenage son, is a schematically disaffected rebel. Ray takes a nap; Rachel orders a hummus plate; Robbie goes AWOL in the Mustang.

Meanwhile, the television reports on a freak lightning storm in Ukraine, and strange clouds mass over the New York skyline. The storm begins. “I thought now would be a good time to send ‘War of the Worlds’ crashing down around everyone’s ears,” Mr. Spielberg says in the press kit. And so he does. A freakishly precise lightning bolt jackhammers into the earth, accompanied by an indescribably intense sonic bombardment.

Ray heads out to investigate, and Mr. Spielberg initiates what may be the greatest of all his action set pieces. A crowd gathers at ground zero of the lightning strike, peering into the crevice. Something rumbles; the pavement begins to split. Mayhem erupts. The facade of the local church splits off and pivots into the street, sunlight shafting through the shattered windows like a death ray blazing from Satan’s skull – a terrible, awe-inspiring image.

A giant robot emerges. Brilliantly computer generated, its steel-bolted form is also somewhat kitsch. Mr. Spielberg has synthesized the H.G. Wells sourcebook via the Cold War sci-fi paradigm, updating rather than rethinking the iconic monster machine. Nevertheless, it’s a knockout baddie, fantastically inhuman. Rising on reptilian legs, it proceeds to laser blast the bejesus out of every mammal in sight. Ray flees the tide of collapsing architecture in a cloud of vaporized bodies.

The sequence, like the entire movie, is rife with evocations of September 11. “War of the Worlds” reflects our fear of domestic attack and anxiety over global conflicts. (Robbie is procrastinating on his term paper on the French occupation of Algeria.) “Is it the terrorists?” worries Rachel, as planes fall from the sky.

But Spielberg being Spielberg, the only thing really at stake is the unquestionable supremacy of the white, middle-class nuclear family. Ray, our hero, is tasked with the survival of his brood. Quickly on foot or careening along in the planet’s last functional minivan, they flee the aliens, hoping to reunite with Mommy in Boston. Along the way, Ray will learn to be a good father.

First, he must allow Robbie to satiate his adolescent revenge impulse by charging the robots alongside the military. Go, Robbie! Throw yourself into that enormous fireball! Had you existed in any known reality, you would now be a useless heap of cinders. How lucky for you to have been born in the magic kingdom of Spielbergia. Welcome to manhood, my improbably intact friend!

Ray’s other important duty is to censor his freethinking daughter’s reality. Rachel is blindfolded, made to stay put, directed not to look at things. Granted, the destruction of the earth isn’t a pretty sight, but this insistent motif is troubling. Mr. Spielberg celebrates forced ignorance. Follow directions, do what you’re told, listen to daddy. It’s for your own good.

While hiding out in a basement for a listless, over-extended sequence, Ray is forced to deal with Ogilvy (Tim Robbins), a crazed survivalist type. Having lost his family to the intergalactic intifada, Ogilvy is now a bachelor, dangerously unstitched from the social fabric. Close your eyes, little Rachel.

The climax, or rather anti-climax of the “War of the Worlds” story has been known for more than a century. The only surprise in this 21st-century telling is the image of an entire planet laid to waste, with the exception of a handsome row of Boston town houses. That may give comfort to some, but even those flattered by this conclusion are likely to find it tonally, stylistically, and dramatically insipid. A strange man, this Steven Spielberg, who surpasses all his audience’s expectations only to insult their intelligence, who grips the public like no one else, then excludes all but the most privileged.

For better and worse, Mr. Spielberg is our Griffith, our Hitchcock: a matchless manipulator of his audience and an unrivaled master of the medium. His control is enthralling, his swiftness exhilarating. No one does special effects better. No one could raise the stakes so high. No one can bring down a storm like this. And no one makes films with the same queasy mix of the formally stupendous and ideologically odious. “War of the Worlds” is a masterpiece of the imagination and a travesty of the social conscience.